IBM 5280 Distributed Data System - Index of

Chapter 4. Object Code Instruction .FormatEach object code instruction is 4 bytes long. The first byte always contains theoperation code. The other three bytes contain flags, addresses and other data.ADDRESSING METHODS WITHIN A PARTITIONIn a source program instruction, a storage area or another instruction is referred toby a label. A register is referred to by a label or by a number. When source instructionis converted to object code, these labels and numbers are converted toaddresses. An address in an object code instruction is always relative to the beginningof the partition. When the object code instruction is executed, the relativeaddress is added to the absolute address of the beginning of the partition. Theabsolute address of the beginning of the partition is stored in displacement hex ODin the partition lOB.Because instructions and registers must begin on specific boundaries, the 16-bitaddress can be compressed. The bits in the object code instruction that are notused for the address are used for other purposes, such as flags. A relative addressin an object code instruction is in one of the following formats:• 16-bit address to locate any byte within a partition• 14-bit address to locate an instruction• 8-bit address to locate a decimal register• 7-bit address to locate a binary registerIn addition to the relative addresses, an object code instruction may contain thefollowing types of data:• 8-bit instruction displacement, used with certain branch instructions to locatean instruction.• 8-bit indicator number to locate an indicator.• 8-bit index into a system table to locate the address of a format, prompt, duplicationarea, or table.• Constant.Object Code I nstruction Format 131